Neoclassical impurities transport induced by 3D fields

The neoclassical impurities transport induced by 3D fields, known as the neoclassical toroidal viscosity (NTV) flux, is discussed in detail using NTVTOK. A substantial inward NTV flux of impurities is observed, which plays a key role in impurity transport and provides a mechanism for the enhancement of impurities intensity induced by resonant magnetic perturbations (RMP). The inward NTV impurities flux results from the negative gap between the E→×B→ drift frequency and the diamagnetic drift frequency of the impurities, a condition that can occur when the impurities gradient is positive. Consequently, this effect is strongly dependent on the spatial distribution of the impurities, in particular the direction and magnitude of the impurities gradient. It is also influenced by the strength of the 3D fields and can be controlled by changing the RMP configuration. The complex dependence of the NTV impurity flux on the toroidal rotation, mass, charge and ion temperature of impurities is also presented and discussed in detail. These factors will alter the collisionality of the impurities, the gap between the E→×B→ drift frequency and the diamagnetic drift frequency, the precession and the bounce-drift resonance, and consequently affect the NTV flux of the impurities. These results improve the understanding of RMP on impurities transport and provide a possible physical basis for the impurities control using RMP.